(1) Field of the Invention
The present invention generally relates to an electronic apparatus having a cooling system, and more particularly to an electronic apparatus having a cooling system which can sufficiently cool a heat source preventing a rise of a noise level.
A electronic apparatus, such as a personal computer, is generally provided with heat sources, such as resistors and a power supply device. Thus, to prevent electronic circuit devices from being damaged by the heat from the heat sources, a cooling system, having a cooling fan, for cooling the electronic circuit devices and the heat sources is provided in the electronic apparatus. It is preferable that the noise level of the operating cooling fan be as low as possible.
(2) Description of the Related Art
In a conventional electronic apparatus, a cooling system is provided as shown in FIG. 1. Referring to FIG. 1, units 11, 12 and 13 and a heat source 14 (e.g. a power supply device) are housed in a housing 10. An intake port 15 and an exhaust port 16 are respectively formed on walls opposite to each other. A cooling fan 20 is mounted in the exhaust port 16 and a temperature sensor 21 is provided near the intake port 15. While the cooling fan 20 is being operated, the air taken into the housing 10 through the intake port 15 flows in spaces among the units 11, 12 and 13 and the heat source 14 as indicated by arrows in FIG. 1. The air is then exhausted through the exhaust port 16. Due to the airflow in the spaces among the units 11, 12 and 13 and the heat source 14, the units 11, 12 and 13 and the heat source 14 are cooled.
The revolving speed of the cooling fan 20 is controlled based on the temperature of the intake air detected by the temperature sensor 21. Examples of a relationship between the controlled revolving speed of the cooling fan 20 and the temperature of the intake air are shown in FIGS. 2A and 2B.
In the case of the relationship shown in FIG. 2A, the revolving speed of the cooling fan 20 is gradually decreased in accordance with a decrease of the temperature of the intake air. That is, the higher the temperature of the intake air, the larger the revolving speed of the cooling fan 20 in order to appropriately cool the units 11, 12 and 13 and the heat source 14, and the lower the temperature of the intake air, the smaller the revolving speed of the cooling fan 20 in order to lower the noise of the cooling fan 20.
In the case of the relationship shown in FIG. 2B, the cooling fan 20 is driven at a high revolving speed in a range of the temperature of the intake air greater than a predetermined value so that the units 11, 12 and 13 and the heat source 14 are appropriately cooled, and is driven at a low revolving speed in a range of the temperature of the intake air less than the predetermined value so that the noise generated by the cooling fan 20 is lowered.
In a case where the cooling fan 20 is driven at the high revolving speed, the air evenly flows in the spaces among the units 11, 12 and 13 and the heat source 14. However, in a case where the cooling fan 20 is driven at the low revolving speed, the air may be partially stagnated in the spaces among the units 11, 12 and 13 and the heat source 14. When the air is stagnated in the spaces, the cooling effect is rapidly lowered. In tis case, if the air around the heat source 14 is stagnated, the temperatures of the respective units and the heat source 14 itself raise.
To prevent the air from being stagnated in the spaces among the units 11, 12 and 13 and the heat source 14, it can be proposed to increase the low revolving speed of the cooling fan 20. However, an increase of the noise generated by the cooling fan 20 results from the increase of the lower revolving speed of the cooling fan 20.